1. Field of the Invention
The present invention relates to an improved process for the manufacture of a metal oxide.
2. Description of the Related Art
When a fine powder of inorganic oxide is produced by an industrial process, a bulk of the inorganic oxide is ground to fine powders more than several microns (.mu.m) in size, and it is difficult to obtain a finer powder by a known grinding process.
Recently, it has become possible to obtain an ultrafine powder material of several hundreds of angstrom (.ANG.) in size by a vapor-phase reaction. However, it is difficult to apply such a method for a production of a bigger powder. There is a demand for a process for manufacturing a powder material with a uniform particle size, i.e., a narrow distribution of a particle size which ranges from 0.1 .mu.m to several microns.
Several attempts have been made to meet such a demand. For example, Takajiro Shimohira mentioned in the Report of the National Institute for Research in Inorganic Materials, Science and Technology Agency, No. 14, pages 49-58, 1977, that, to produce SiO.sub.2 powder, a certain amount of ethyl silicate and a certain amount of an aqueous ammonia are reacted batchwise to grow the powder to about 0.3 .mu.m while realizing a narrow distribution of the uniform particle size.
In the above method, however, a concentration of alkoxide must be raised to increase the particle size, and this raising of the concentration can affect the uniformity of the size distribution. Therefore, a range of the concentration which is practically operable is extremely limited.
To solve this problem, an attempt was made wherein fine powder materials produced by the above process and having a narrow distribution of the particle size were introduced into a fresh reaction system, with the intention of growing the powder in a batchwise reaction by using the fine powder materials as a core. However, the growth of the powder materials was accompanied by a formation of fresh grains, and thus the size distribution was adversely affected.
In addition to SiO.sub.2 powder, there were attempts to produce an inorganic oxide powder with a narrow distribution of size by a batchwise reaction, but a successful method of controlling the size distribution has not been found. As stated above, it is difficult to obtain a powder material having a narrow distribution of size ranging from 0.1 .mu.m to several microns, by a batchwise reaction.